1. Field of the Invention
The invention relates to a communication system with a plurality of subscribers which are connected by means of an interface circuit to a ring feeder for the common transmission of digital source data and control data; the source data and control data are transmitted in a format which prescribes a pulsed sequence of individual bit groups of equal length which are subdivided into component bit groups which form a respective data channel; at least one data channel is provided for control data which are transmitted in data packets with a destination address; the interface circuit of each subscriber contains an address decoder.
Such communication systems are used wherever different types of electric and electronic devices which are to exchange information with one another in a partially complicated way are networked to one another by means of data lines of physically simple design. The subscribers can exchange both source data and control data via these data lines. For example, in an audio application it is possible to transmit audio data from data sources such as CD players, radio receivers and cassette players to data sinks such as amplifier/loudspeaker combinations, and control data can be transmitted at the same time, for example to control the volume of the system. In this case, a device can be designed simultaneously as a data source and a data sink, such as is the case with a cassette recorder, for example.
2. Description of the Related Art
A method for the common transmission of source data and control data between data sources and data sinks connected via data lines is described in general in European patent disclosure EP 0 725 522 (incorporated by reference). The method is also described in the printed publication "OCC8001 `CONAN` OPTICAL TRANSCEIVER", C&C Electronics Ltd., 1996, which shows in detail an interface circuit for connecting individual subscribers to the ring feeder. Since the interface circuit does not have its own intelligence, it is capable of operating only in combination with a microcontroller, a microprocessor set up for the special control tasks in the system, which is capable of interpreting an instruction communicated within the framework of control data in accordance with the protocol used in the system, and which then controls the interface circuit or a subscriber associated therewith in accordance with the instruction.
The correct interpretation of the instructions in the microcomputer presupposes that the microcomputer of all the subscribers of the communication system has a standard protocol. If the functionality of the system is changed, for example by adding a new subscriber, it is also necessary to recreate or change the instruction interpreter.